The present invention relates generally to an electrical contact for press-fit mounting in a plated-through hole in a printed circuit board substrate and, more particularly, to an electrical contact with a mounting section having an oblong base portion and one or more flexible fins attached to the circumference of and extending in the longitudinal direction of the base portion and a method for making such a contact.
Electrical contacts which are press-fit mounted in plated-through holes of printed circuit boards without need for soldering have become widely used in the electronics industry. Such electrical contacts are commonly referred to as press-fit terminals. Examples of such press-fit terminals are the H-shaped press-fit pin manufactured by the assignee of the present application and disclosed, for example, in U.S. Pat. No. 4,728,164 granted Mar. 1, 1988; the "Bow-Tie" press-fit pin, also manufactured by the assignee of the present application and disclosed, for example, in U.S. Pat. No. 4,274,699 granted Jun. 23, 1981; the "Action Pin", manufactured by AMP and disclosed, for example, in U.S. Pat. No. 4,186,982; and the "C-press" pin manufactured by the Winchester Electronics Division of Litton Systems, Inc. disclosed, for example, in U.S. Pat. No. 4,017,143 granted Apr. 12, 1977.
U.S. Pat. No. 4,728,164 noted above discloses an electrical contact pin for mounting in the plated-through holes of a printed circuit board through compliant press-fit action. The mounting section has an H-shaped cross-section which comprises four compliant fins and a central crossbar. The contact pin is made from square wire or flat strip material and its H-shaped mounting section is formed by stamping or other suitable mechanical deformation techniques. The fins are therefore formed integrally with and are of the same metal as the crossbar, having been forced outward or extruded during stamping.
U.S. Pat. No. 4,464,009 granted Aug. 7, 1984 describes a solderless contact pin wherein the deformable mounting section is M-shaped or W-shaped. The mounting section is also formed by stamping and consists of two elongated beam members interconnected integrally to one another by a cross-member.
Insertion and retention of a press-fit terminal in place in a circuit board hole requires very accurate dimensioning of the mounting seciton. This is of great importance. If the mounting section is too small compared to the opening of the substrate, the electrical contact with the metallized wall of a plated-through hole may be unreliable. Also, the retention force applied to the wall of the hole to keep the terminal in place may not be sufficient. On the other hand, too large a mounting section may cause serious damage to the metallized layer of the wall in the hole and consequently also lead to an unreliable electrical connection. It may cause twisting or shifting during mounting of the terminal in relation to the desired position.
The requirements for accurate dimensioning become even more critical when the size of the opening of the substrate decreases. In practice, it has become evident that the prior art electrical contacts with mounting sections produced by mechanical deformation such as stamping are inadequate for smaller hole dimensions unless one is willing to accept a relatively high waste percentage. It should be pointed out that accurate dimensioning of the mounting section is always necessary to achieve the required firm mechanical mounting and, if applicable, also a reliable electrical connection.
Rather than a mounting section of integrally formed members deformed through stamping and the like, U.S. Pat. No. 4,684,203 granted Aug. 4, 1987 discloses an electrical contact pin wherein one or two separate contact springs are attached to one or two lateral surfaces of the base pin. The mounting section of the base pin is flattened by pressing to provide two opposite flat surfaces. Separately formed and outwardly curved contact springs are then attached to each flat surface by welding one end of each contact spring to the base pin. The contact springs extend longitudinally along the length of the base pin and are outwardly curved or convex so that each is furthest from the flat lateral surface of the pin at the spring's mid-point. The contact springs are subjected to bending stress as the convex curve is forced by the hole wall to flatten against the flat lateral surfaces of the contact pin as the latter is inserted into the printed circuit board hole. This patent discloses that its contact pin package is designed for holes having a nominal diameter of 0.889 mm to 1.143 mm (0.035"to 0.045"), or approximately the maximum range of conventional printed circuit board holes, which typically have a nominal diameter of about 0.040 inches or about 1 mm.